In response to environmental and economic concerns, developing public policy throughout the world emphasizes the increased recycling of waste materials. The U.S. Environmental Protection Agency has recommended that twenty-five percent of solid wastes should be recycled. Various states have passed laws mandating the recycling of certain wastes. Certain industries, the plastics industry in particular, are promoting the increased recycling of materials, including the development of new technologies and markets for recycled products.
Solid carbon may be produced in a variety of physical forms, including a form known in the field as carbon black. This latter form of solid carbon is used in the fabrication and manufacture of many items including automobile tires, paints, and audio and video tapes.
Typically, the "bottoms," or waste oil, from refineries have been used in the manufacture of carbon black. The conventional manufacturing process for carbon black from waste oil requires the use of special reactors, high temperatures, and the combustion of fossil fuels. The cost of manufacturing carbon black by the conventional type of process has been on the order of $0.20 per pound. Average industrial prices for carbon black are in the range of $0.20 to $0.26 per pound.
Hydrogen in its elemental form is an extremely light gas which is also highly flammable. Hydrogen is an excellent fuel because of the large amount of energy produced per unit mass of hydrogen consumed in a combustion reaction with oxygen. Hydrogen is further desirable as a fuel because, when it undergoes oxidation, the only product of this reaction is water vapor which is completely non-polluting. Because of these desirable characteristics, it is used, for example, in fuel cells to produce energy.
The problem of managing the wastes produced by industry, hospitals, and homes is quickly reaching crisis proportions. The use of landfills, the traditional waste disposal method in the United States, now must be considered the method of last choice. Existing landfills are nearly at capacity. Many are leaking and, as a result, are polluting groundwater, and many could eventually end up as Superfund sites. Furthermore, as a matter of political reality, it is almost impossible to establish new landfills to replace those existing landfills now nearly at capacity.
Incineration has increasingly become the waste disposal method of choice for industry. Community resistance to incineration, however, is strong and steadily increasing because of the amounts of toxic organic chemicals, such as dioxins and furans, and of toxic heavy metals, emitted by incinerators, and because of other difficulties associated with the operation of incinerators. In addition, incinerators are expensive, and their use has resulted in a large increase in the cost of waste treatment. As a practical matter, obtaining the required government permits for new incinerators has also become as difficult as obtaining the permits for new landfills.
As the environmental requirements for landfills are increased and the use of incineration increases, the cost for the management of wastes increases as well. For example, solid waste costs increased by a factor of three in the one year from 1988 to 1989 in Pittsburgh and now are generally between $75 and $150 per ton in New Jersey and other Northeastern States. Costs for disposal of hazardous wastes and medical wastes are greater, typically exceeding $300 per ton.
Incinerators and incinerator-type waste treatment technologies use high temperature oxidation, or burning, of organic materials as the basic means of waste treatment. Optimally, these types of processes result primarily in the production of carbon dioxide and water as products of the treatment process. Small amounts of other materials are produced depending upon the elements present in the feed materials. However, there are basic problems associated with combustion-based incinerators in that they are difficult and expensive to operate and that they create potentially hazardous hydrocarbon species through incomplete combustion.
Hobbs U.S. Pat. No. 3,648,630 and Hardison et al. U.S. Pat. No. 4,667,609 describe incinerators that use infrared radiation from black body radiators to heat solids as a means to promote combustion, or oxidation, of the waste materials with which the solids are contaminated. The basic process in these incinerators, combustion, is the same as in incinerators which use the burning of fossil fuels as a means to heat the waste materials to combustion temperatures.
A proposed solution to the problems of incineration is described in Matovich U.S. Pat. No. 3,933,43. The Matovich patent discloses a high temperature fluid-wall waste-treatment device for wastes containing up to 10 percent organics, in which the energy required is supplied to a chemical reactor by radiation. Matovich's high temperature fluid wall reactor (HTFWR) is a once-through, vertical tube reactor. After preprocessing, which for solids is an extensive operation that reduces the solid matter to 50-100 mesh size, the raw materials are introduced into the top of the reactor and fall within a hollow, porous carbon core to the bottom outlet of the reactor. Matovich's HTFWR is heated electrically by resistance heaters or by other means located outside the hollow, porous carbon core. The heaters are radiatively coupled to the hollow, porous carbon core and heat the core radiatively. The raw materials falling within the hollow core are heated by radiation from the core.
Even though it does not rely primarily on oxidation reactions, the Matovich device has other serious shortcomings. One shortcoming is that all solid material to be treated must first be processed to extremely small size (less than about 100 mesh) so that the particles will remain within the radiation zone for a sufficiently long time to decompose. Another drawback of the Matovich device is that it requires a continual flow of nitrogen gas through the reactor, the fluid wall, to protect the heaters, insulation and walls from oxidation and damage from molten materials. The fluid wall forms a reaction chamber within the interior of the hollow, porous carbon core, thereby protecting the surface facing toward the interior of the core from becoming damaged by molten inorganic materials. The presence of the undesirable fluid wall adds considerable expense to the operation of the Matovich device.
Still another approach to overcoming the problems with incineration is the Electric Pyrolyzer, a system that was developed by the Westinghouse Electric Corporation, and that may be used at temperatures as high as 3000.degree. F., and in a low oxygen environment, to process predominantly inorganic wastes such as contaminated soils that have no more than a 10% composition by mass of organic contaminants. See, in this regard, the report on pages 4-12 through 4-14 in the May/June 1988 edition of The Hazardous Waste Consultant.
Both the Matovich and the Westinghouse devices, in addition to other shortcomings in their operation, cannot recycle the treated waste into useful forms such as solid carbon and hydrogen gas.
Accordingly, it is an object of the present invention to provide a method of recycling of organic waste materials, including non-pretreated infectious hospital waste, refinery waste, waste paper, food processing waste, and other similar solid, liquid, and gaseous wastes, by decomposing the organic content of these wastes primarily into carbon, which forms as a powder, and hydrogen.
A related object of the present invention is to provide a method in which the organic waste materials are recycled through decomposition into their constituent elements by absorption of radiant energy.
Another objective of the present invention is to provide a system with a suitable environment such that the use of inert gases is not required and such that unwanted chemical reactions are avoided through the use of a substantially closed system produced by recycling the exhaust gases, thereby producing an environment consisting predominantly of hydrogen within the system.
A further related object of the present invention is to provide a method in which pretreatment of the waste materials is not required, and a minimum amount of size reduction of materials is necessary to allow the waste materials to be readily introduced into the reactor.
A still further object of the present invention is to provide a method in which the carbon and hydrogen can be removed from a stream of exhaust gases from the reactor without first requiring extensive processing to substantially cool the exhaust gas stream.
Still another object of the present invention is to provide a method which employs a closed reactor system in which the exhaust gas stream is recycled to the reaction chamber so that whatever small amount of gases are eventually released to the environment are substantially free from potentially harmful hydrocarbon molecules.